1. Field of the Invention
The present invention relates to a valve opening and closing control apparatus, which drives a valve.
2. Description of Related Art
In order to reduce noxious components (e.g., nitrogen oxide also called as NOx) contained in the exhaust gas outputted from each combustion chamber of the internal combustion engine (e.g., a diesel engine), an exhaust gas recirculation apparatus, which includes an exhaust gas recirculation pipe and an EGR control valve, has been proposed (see, for example, Japanese Unexamined Patent Publication No. 2005-233063). The exhaust gas recirculation pipe recirculates a portion of the exhaust gas, which is outputted from each combustion chamber of the internal combustion engine, into an intake system of the internal combustion engine. The EGR control valve variably controls a recirculation quantity of the EGR gas (an EGR quantity) flowing in the exhaust gas recirculation pipe.
As shown in FIG. 6, the EGR control valve, which is installed in the exhaust gas recirculation apparatus, includes a housing 101, a nozzle 103, a butterfly valve 105, a valve shaft 106 and an actuator. The housing 101 forms a portion of the exhaust gas recirculation pipe. The nozzle 103 is fitted into and is supported by a cylindrical portion 102 of the housing 101. The butterfly valve 105 is received in an interior (an exhaust gas passage 104) of the nozzle 103 such that the butterfly valve 105 can be opened and closed therein. The valve shaft 106 supports the butterfly valve 105. The actuator drives the butterfly valve 105 through the valve shaft 106 to execute the valve opening movement and the valve closing movement of the butterfly valve 105.
A single coil spring, in which a first spring 111 and a second spring 112 are integrated together, is provided as a valve urging means of the EGR control valve. The first spring 111 applies a spring load to the butterfly valve 105 in the valve closing direction, and the second spring 112 applies a spring load to the butterfly valve 105 in the valve opening direction. One end portion of the first spring 111 and the other end portion of the second spring 112 are wound in opposite directions, respectively.
The actuator includes an electric motor (serving as a drive source) 107 and a speed reducing gear mechanism. The speed reducing gear mechanism reduces the rotational speed of a motor shaft 109 in two steps and thereby increases the drive force (the rotational torque) of the motor 107 to drive the valve shaft 106 of the butterfly valve 105. The speed reducing gear mechanism includes first to third gears 121-123.
The first gear 121 is a motor gear, which is fixed to the motor shaft 109 of the motor 107 and is rotated about an axis of the motor shaft 109. The second gear 122 is an intermediate speed reducing gear, which is rotated about an axis of a gear shaft 124, which is securely press fitted into the housing 101. The second gear 122 includes a large diameter gear and a small diameter gear, which are formed integrally. The large diameter gear is meshed with the first gear 121, and the small diameter gear is meshed with the third gear 123. The third gear 123 is a valve gear, which is fixed to the valve shaft 106 of the butterfly valve 105 and is rotated about an axis of the valve shaft 106. In general, a predetermined gap (backlash) is required between opposed tooth surfaces of adjacent gears to enable smooth movement of the gears.
The exhaust gas, which is outputted from each combustion chamber of the internal combustion engine, contains fine particulate impurities (exhaust fine particles, particulate matter), such as combustion residues or carbon particles. Thus, a deposit (attachment or sediment) of the particulate impurities contained in the exhaust gas may possibly be attached or accumulated in the interior of the EGR control valve during the operation of the internal combustion engine.
In the case where the deposit is adhered or accumulated around the valve of the EGR control valve, when a viscosity of the deposit becomes relatively high upon dropping of the temperature of the deposit after engine stop, valve sticking (sticking of the valve caused by the viscous deposit) may possible occur due to the solidification of the deposit.
In the case of the EGR control valve recited in Japanese Unexamined Patent Publication No. 2005-233063 (corresponding to U.S. Pat. No. 7,234,444), in order to limit the sticking of the butterfly valve 105 caused by the accumulation and solidification of the deposit, the butterfly valve 105 is driven by the drive force of the motor 107 to execute the opening and closing movement of the butterfly valve 105 over the valve full close position at least once and is then stopped at the valve stop position after passing the valve full position. In this way, the deposit, which is adhered or accumulated around the valve 105, is scraped from a passage wall surface of the nozzle 103 around the valve full close position.
Furthermore, there is also known an EGR control valve, in which the butterfly valve 105 is driven to execute the opening and closing movement of the butterfly valve 105 at least once within a predetermined range, which extends from a location before the valve full close position and a location after the valve full close position, and then the butterfly valve 105 is stopped at the valve full close position, so that the deposit, which is adhered or accumulated on the passage wall surface of the housing 101, is scraped (see, for example, Japanese Unexamined Patent Publication No. 2003-314377).
In the EGR control valves recited in Japanese Unexamined Patent Publication No. 2005-233063 (corresponding to U.S. Pat. No. 7,234,444) and Japanese Unexamined Patent Publication No. 2003-314377, when the butterfly valve 105 is reciprocally moved between the two target positions in the deposit scraping action over the neutral position, at which the spring load of the first spring 111 and the spring load of the second spring 112 are balanced with each other, a relatively large hitting sound (collision sound) is generated due to collision between tooth surfaces of the adjacent gears. This is due to reversing of the direction of the backlash between the tooth surfaces of the first and second gears 121, 122 and reversing of the direction of the backlash between the tooth surfaces of the second and third gears 122, 123 at the time of passing through the neutral position.
Since this hitting sound is the impact sound, the hitting sound may possibly be reduced by reducing the valve moving speed throughout its movement. When the valve moving speed is reduced, the time required for the deposit scraping action is disadvantageously lengthened. Thereby, the time between the turning off of the ignition switch and turning off of a main relay of an engine control unit (ECU) is lengthened. Thereby, a risk in terms of a vehicle burglar security is disadvantageously increased in a vehicle having a burglarproof security system.
In the deposit scraping action, when the movement of the butterfly valve 105 is set such that the butterfly valve 105 does not move over the neutral position, the hitting sound, which is caused by the collision between the tooth surfaces of the gears, is not generated. However, in such a case, the valve stop position at the time of stopping the power supply to the motor 107 is deviated from the valve full close position. Therefore, the butterfly valve 105 is placed in the open state. Thereby, at the time of failure of the EGR control valve, i.e., at the time of failure of the motor 107, the EGR gas is always recirculated into the intake system of the internal combustion engine. Thus, the EGR quantity may possibly become excessive relative to the intake air quantity. When the EGR quantity becomes excessive relative to the intake air quantity, a misfire of the internal combustion engine may occur. This may lead to an engine stall, and thereby the vehicle may not be driven.